Aluminum soap thickeners with surface active agents



United States Patent 3,539,311 ALUMINUM SOAP THICKENERS WITH SURFACEACTIVE AGENTS Leonard Cohen, Baltimore, Md., and William T. Gregory,

Rushville, Ill., assignors to the United States of America asrepresented by the Secretary of the Army N0 Drawing. Filed June 8, 1955,Ser. No. 514,136 Int. Cl. C101 7/02 US. Cl. 44-7 6 Claims The inventiondescribed herein may be manufactured and used by and for the Governmentof the United States of America for governmental purposes without thepayment to us of any royalty thereon.

This invention relates to the thickening of gasoline by aluminum soaps.

Gasoline, thickened or gelled by small quantities (about 1 to 12%) ofaluminum soaps of higher carboxylic acids, is important as an incendiaryin warfare. Various aluminum soaps have been used, the best-known beingnapalm, the aluminum soap of a mixture of oleic and naphthenic acids andcoconut-oil fatty acids, disclosed and claimed in US. Pat. No. 2,606,107to Louis F. Fieser. More recently, improved results have been obtainedby the use of about 0.75 to 4% of aluminum octoates, notably aluminumdi- (2-ethyl hexoate) and the isooctoates disclosed in applications,Ser. Nos. 321,747 and 466,242, filed Nov. 20, 1952 and Nov. 1, 1954,respectively, by Leonard Cohen, now Pats. 2,741,629 and 2,718,462,respectively.

One advantage of these thickened gasolines over other incendiary fuelslies in the fact that they may be produced in the field by mixing thedry soap with gasoline. The proper amount of soap is added to a batch ofgasoline and the mixture agitated until thickening occurs. The gel isthen allowed to stand, or cure, for a certain length of time. During thecuring period the gel develops elasticity.

It is desirable that the time of mixing, or vortex time, and the curetime be as short as possible, particularly to make it possible to usecontinuous rather than batch mixing and to make prompt use of the filledbombs or flamethrowers. It is also desirable that the gel be as high inconsistency as possible for a given amount of thickening agent, that itbe highly elastic, and that it be stable over a long period of time.

In application Ser. No. 514,135 filed June 8, 1955 by us jointly withLeo Finkelstein and Sidney Magram, we have shown that the vortex timeand the cure time can be shortened, while retaining or enhancing theother desirable properties, by adding to the gasoline prior to theaddition of the aluminum soap, a small amount of a nonionicsurface-active agent, prefera'bly accompanied by water, particularlywhen the aluminum soap is aluminum hydroxy di 2-ethyl hexoate) We havealso found that similarly improved results can be obtained by adding asmall amount of a fatty acid having at least three carbon atoms, thosehaving from six to being preferred. The straight-chain acids were foundto be most effective, notably caproic, heptoic, caprylic, pelargonic andcapric acids. The branched-chain acids such as Z-ethyl butyric, 2-ethylhexoic, and 3,5,5-trimethyl hexoic were somewhat less effective than thestraight-chain acids.

An essential feature of our invention is the addition with the acid ofsmall amounts of water, the ratio of water to acid ranging from 10:90 to:85. In the case of the higher acids it may be desirable to employ acosol- 3,539,311 Patented Nov. 10, 1970 vent in order to maintain themutual solubility of water and acid over a wide temperature range.Isopropanol and the diethyl ether of ethylene glycol are suitablecosolvents. Suitable blends for the addition to gasoline may have thefollowing compositions (by weight) 2 Fatty acid: H O: 15% 10%Cosolvent:- 100% Such a blend has proved effective in the proportion ofabout 1 part blend to 10 parts aluminum soap.

While the peptization of aluminum soaps by fatty acids to hasten theformation of hydrocarbon gels has been previously known, the use ofsmall amounts of water produces very different and improved results andis believed to involve a completely different mechanism. Whereaspeptization of aluminum soaps by fatty acids involved the use of acidand soap in a minimum effective ratio of 1:4, by weight, the addition ofthe water permits the use, as noted above, of an acid/water/cosolventblend in a ratio of blend to soap of only 1:10, by Weight. Since theblend is less than 50% acid, this means that the ratio of acid to soapis less than 1:20.

Still more important is the change in the gel itself. The use of acidalone as peptizer causes a reduction in the consistency of the gel asmeasured by a Gardner Mobilometer, while the use of an acid blend withwater causes an increase of gel consistency due to improved curing ofthe gel.

It is believed that the mechanism of interaction between surface-activeagents or fatty acids involving the use of water differs completely fromsimple peptization of aluminum soaps by polar compounds such as fattyacids in the formation of hydrocarbon gels. In the process ofpeptization it has been found that the aluminum soap micelles arereduced in size and molecular weight by the action of the chemicallypolar peptizer, thereby rendering them more readily soluble inhydrocarbons with a resulting decrease of gel consistency. In theprocess of formation of aluminum soaps by aqueous metathesis from sodiumsoap and aluminum salts in the presence of excess sodium hydroxide,aluminum hydroxide is formed with the aluminum soap. This aluminumhydroxide is hydrophilic in nature and obstructs access of thehydrocarbons to the aluminum soap thereby retarding gelation. It isbelieved that the addition of surface-active agents or acids containingwater causes hydration and addition "by chemisorption of the lipophilicagent or acid to the surface of the aluminum hydroxide, therebyeliminating the obstruction of access to the aluminum soap by thehydrocarbon solvents. While we believe the above explanation to becorrect, we do not Wish to be bound by theory.

The following example shows the improvement produced by our invention:

EXAMPLE In a laboratory mixer, four percent of aluminum hydroxydi-(2-ethyl hexoate), which-had been formed by reacting aluminum sulfateor aluminum chloride and sodium 2-ethyl hexoate in an aqueous solutionof sodium hydroxide, was added to gasoline and the electric stirrerrotated at a fixed speed. As the mixture thickens, the level of thevortex rises about the rod of the stirrer. The time was noted for thelevel to rise from a predetermined initial level to a fixed point on therod. This time is used as the vortex time. While the test is empiricalin its choice of conditions, it is useful because it gives aquantitative measure of the time a thickener must be mixed in the fieldbefore it is allowed to stand or cure. The cure time was then determinedby allowing the mixture to stand and noting the point at whichelasticity develops.

Finally, the gel was allowed to stand for 24 hours and the consistencywas then determined using a Gardner Mobilometer.

The experiment was then repeated in the same manner except that therewas first added to the gasoline 0.4%, by weight, an acid/water/cosolventblend, as described above, prior to the introduction of the aluminumsoap.

Results of the tests are shown in the following table:

Ratio, water acid Vortex Gardner time, Curetime, consistency minutesminutes after 24 hrs.

Acid

None (control) O p Heptoic z 12288 Capryllc {010:90

cno

Pelargonic {gigzgg Cap1'ic 10592 num hydroxy di-(Z-ethyl hexoate), theamount of said aluminum hydroxy di-(Z-ethyl hexoate) being about one totwelve percent by weight of the gasoline and the amount of thefirst-named fatty acid being about five percent by weight of thealuminum di-(Z-ethyl hexoate), stirring the mixture until thickeningoccurs, and then allowing the thickened mixture to stand until itdevelops elasticity.

2. A process as defined in claim 1 wherein the firstnamed fatty acid isa straight-chain acid.

3. A process as defined in claim 1 wherein the firstnamed acid iscaproic acid.

4. A process as defined in claim 1 wherein the firstnamed acid iscaprylic acid.

5. A process as defined in claim 1 wherein the firstnamed acid ispelargonic acid.

6. A process as defined in claim 1 wherein the firstnamed acid is capricacid.

References Cited UNITED STATES PATENTS 2,390,609 12/1945 Minich 252-3162,492,173 12/1949 Mysels 44-7 X 2,718,462 9/1955 Cohen 447 2,751,2846/1956 Hill.

FOREIGN PATENTS 544,729 4/ 1942 Great Britain.

LELAND A. SEBASTIAN, Primary Examiner U.S. Cl. X.R.

1. A PROCESS OF GELLING GASOLINE COMPRISING ADDING TO SAID GASOLINE ABLEND OF WATER AND A FATTY ACID CONTAINING FROM 6 TO 10 CARBON ATOMS PERMOLECULE, THE RATIO OF WATER TO ACID RANGING FROM 10:90 TO 15:85 THENADDING ALUMINUM HYDROXY DI-(2-ETHYL HEXOATE), THE AMOUNT OF SAIDALUMINUM HYDROXY DI-(2-ETHYL HEXOATE) BEING ABOUT ONE TO TWELVE PERCENTBY WEIGHT OF THE GASOLINE AND THE AMOUNT OF THE FIRST-NAMED FATTY ACIDBEING ABOUT FIVE PERCENT BY WEIGHT OF THE ALUMINUM DI-(2-ETHYL HEXOATE),STIRRING THE MIXTURE UNTIL THICKENING OCCURS, AND THEN ALLOWING THETHICKENED MIXTURE TO STAND UNTIL IT DEVELOPS ELASTICITY.